Clinical relevance of ATP-dependent potassium channels.

Many cells are equipped with so-called potassium (K+) channels which have an important role in maintaining transmembrane potential. Closure of these channels leads to membrane depolarization, which can be followed by cell-specific activity such as contraction of vascular smooth muscle, or secretion of insulin from pancreatic beta-cells. Therefore, it is not surprising that a number of drugs have been introduced which influence K+ channels by either blocking or opening them. The treatment of type 2 (non-insulin-dependent) diabetes mellitus with sulphonylurea derivatives (SU), which exert their insulinotropic effect by closing the K+[ATP] channels of the pancreatic beta-cell, is customary. Slight differences are described in the insulinotropic action of the various SU. Claims in the past that treatment with SU increases cardiovascular mortality are not supported by sound evidence. SU may even reduce cardiovascular mortality by protecting against ventricular arrhythmias during cardiac ischaemia. K+[ATP]-channel-opening drugs are under investigation for the treatment of essential hypertension and angina pectoris. They are at least as effective in achieving adequate blood pressure control as calcium channel blockers. The recently introduced coronary vasodilating drug, nicorandil, exerts its effect by two mechanisms of action: opening K+[ATP] channels in vascular smooth muscle cells of coronary arteries and activation of guanidyl cyclase by its nitro-group in these cells. A proarrhythmic effect of K+[ATP] channel openers has only been observed at very high doses, but not in the low doses used in angina pectoris and hypertension. In vivo no negative effect of K+[ATP]-channel-opening drugs on insulin secretion is found.